Magnetic Field Sensor For Detecting An Absolute Position Of A Target Object

ABSTRACT

A magnetic field sensor for sensing an absolute position of a target object can include one or more magnetic field sensing elements disposed proximate to a mechanical intersection of first and second portions of a target object, wherein the one or more magnetic field sensing elements are operable to generate a first magnetic field signal responsive to the movement of both the first and second portions. The magnetic field sensor can also include a position detection module operable to use the first magnetic field signal to generate a position value indicative of the absolute position. The magnetic field sensor can also include an output format module coupled to receive the position value and to generate an output signal from the magnetic field sensor indicative of the absolute position.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors, and, moreparticularly, to a magnetic field sensor that can detect an absoluteposition (e.g., a rotation absolute angle) of a target object.

BACKGROUND

Various types of magnetic field sensing elements are known, includingHall Effect elements and magnetoresistance elements. In contrast,magnetic field sensors generally include a magnetic field sensingelement and other electronic components. Some magnetic field sensorsalso include a permanent magnet (a hard ferromagnetic object) in aso-called “back biased” arrangement described more fully below. With aback-biased arrangement, a moving ferromagnetic object can causefluctuations in the magnetic field of the magnet, which is sensed by theback biased magnetic field sensor. Other magnetic field sensors cansense motion of a magnetic target object.

Magnetic field sensors provide an electrical signal representative of asensed magnetic field. In some embodiments that have the magnet(back-biased arrangements), the sensed magnetic field is a magneticfield generated by the magnet, in which case, in the presence of amoving ferromagnetic object, the magnetic field generated by the magnetand sensed by the magnetic field sensor varies in accordance with ashape or profile of the moving ferromagnetic object. In contrast,magnetic field sensors that sense a moving magnet directly sensevariations of magnetic field magnitude and direction that result frommovement of the magnet.

Magnetic field sensors (back-biased) are often used to detect movementof features of a ferromagnetic gear, such as gear teeth and/or gearslots or valleys. A magnetic field sensor in this application iscommonly referred to as a “gear tooth” sensor.

In some arrangements, the ferromagnetic gear is placed upon an object,for example, a camshaft in an engine or the shaft of an electric motor.Thus, it is the rotation of the object (e.g., camshaft) that is sensedby detecting the moving features of the ferromagnetic gear. Gear toothsensors are used, for example, in automotive applications to provideinformation to an engine control processor for ignition timing control,fuel management, anti-lock braking systems, wheel speed sensors,electric motor commutation and other operations.

With regard to electric motors, information provided by the gear-toothsensor to an electric motor control processor can include, but is notlimited to, an absolute angle of rotation of an object (e.g. a motorshaft) as it rotates, a speed of the rotation, and a direction of therotation. With this information the e-motor control processor can adjustthe timing of commutating different magnetic coils of the motor.

However, in some electric motor drive applications, the gear toothsensor does not provide accurate enough determination of angle ofrotation, i.e., position, and direction of rotation of the electricmotor shaft. One such application is for main drive electric motors usedin electrical automobiles.

In some electric motor drive applications, a plurality of magnetic fieldsensing elements, e.g., three Hall elements, are used in relation to aplurality of windings of a multi-phase electric motor, which has aplurality of motor windings, in order to sense a position of theelectric motor shaft. With this arrangement, an electric motor controlprocessor can use signals from the plurality of magnetic field sensingelements to generate a plurality signals with proper phases communicatedto the plurality of motor windings. However, in some electric motordrive applications, the plurality of magnetic field sensing elementsalso does not provide accurate enough determination of angle ofrotation, i.e., position, and direction of rotation of the electricmotor shaft.

Applications for which more accuracy is desired include, but are notlimited to, main drive electric motors used in electrical automobiles.

Thus, it would be desirable to provide a magnetic field sensor that canidentify, with improved accuracy, a rotational angle, i.e., a position,or a linear position of a target object as the target object moves. Thetarget object can be coupled to, but is not limited to being coupled to,a shaft of an electric motor.

SUMMARY

The present invention provides a magnetic field sensor that canidentify, with improved accuracy, a rotational angle, i.e., a position,or a linear position of a target object as the target object moves. Thetarget object can be coupled to, but is not limited to being coupled to,a shaft of an electric motor.

In accordance with an example useful for understanding an aspect of thepresent invention, a magnetic field sensor for sensing an absoluteposition of a target object, wherein the target object has a firstportion having a first quantity of target features and a second portionhaving a second quantity of target features different than the firstquantity, wherein the first and second portions are proximate andmechanically fixed together, wherein the target object, including thefirst and second portions, is capable of a movement, the magnetic fieldsensor can include:

one or more magnetic field sensing elements disposed proximate to amechanical intersection of the first and second portions of the targetobject, wherein the one or more magnetic field sensing elements areoperable to generate a first magnetic field signal responsive to themovement of both the first and second portions;

a position detection module operable to use the first magnetic fieldsignal to generate a position value indicative of the absolute position;and

an output format module coupled to receive the position value and togenerate an output signal from the magnetic field sensor indicative ofthe absolute position.

In accordance with an example useful for understanding another aspect ofthe present invention, a method of sensing an absolute position of atarget object, wherein the target object has a first portion having afirst quantity of target features and a second portion having a secondquantity of target features different than the first quantity, whereinthe first and second portions are proximate and mechanically fixedtogether, wherein the target object, including the first and secondportions, is capable of a movement, the method can include:

generating a first magnetic field signal responsive to the movement ofboth the first and second portions;

using the first magnetic field signal to generate a position valueindicative of the absolute position; and

generating an output signal from the magnetic field sensor indicative ofthe absolute position.

In accordance with an example useful for understanding another aspect ofthe present invention, a magnetic field sensor for sensing an absoluteposition of a target object, wherein the target object has a firstportion having a first quantity of target features and a second portionhaving a second quantity of target features different than the firstquantity, wherein the first and second portions are proximate andmechanically fixed together, wherein the target object, including thefirst and second portions, is capable of a movement, the magnetic fieldsensor can include:

means for generating a first magnetic field signal responsive to themovement of both the first and second portions;

means for using the first magnetic field signal to generate a positionvalue indicative of the absolute position; and

means for generating an output signal from the magnetic field sensorindicative of the absolute position.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is an isometric drawing showing a side view of a magnetic fieldsensor proximate to a target object, the target object having first andsecond portions, wherein the first and second portions have differentnumbers of target features, and wherein the magnetic field sensor hasfirst one or more magnetic field sensing elements disposed proximate tothe first portion and second one or more magnetic field sensing elementsdisposed proximate to the second portion;

FIG. 2 is a pictorial diagram showing a top view of the magnetic fieldsensor and target object of FIG. 1;

FIG. 3 is a graph showing illustrative signals generated by the firstand second one or more magnetic field sensing elements of FIG. 1, andalso thresholds that can be used to detect angular position of thetarget object when the target object rotates;

FIG. 4 is a block diagram showing an illustrative magnetic field sensorproximate to two target object portions, here shown to be separate, thatcan be like the magnetic field sensor and two portions of FIGS. 1 and 2,which can generate the signals of FIG. 3, and which can have a phasedifference module operable to identify a phase difference between thesignals of FIG. 3;

FIG. 5 is a block diagram showing further details of an illustrativephase difference module according to FIG. 4;

FIG. 6 is a block diagram showing further details of anotherillustrative phase difference module according to FIG. 4;

FIG. 7 is a block diagram showing further details of anotherillustrative phase difference module according to FIG. 4;

FIG. 8 is a block diagram showing another illustrative magnetic fieldsensor proximate to two target object portions, here shown to beseparate, that can be like the magnetic field sensor and two portions ofFIGS. 1 and 2, which can generate the signals of FIG. 3, and which canhave a phase difference module operable to identify the phase differencebetween the signals of FIG. 3;

FIG. 9 is a block diagram showing another illustrative magnetic fieldsensor proximate to two target object portions, here shown to beseparate, that can be like the magnetic field sensor and two portions ofFIGS. 1 and 2, which can generate the signals of FIG. 3, and which canhave a phase difference module operable to identify the phase differencebetween the signals of FIG. 3;

FIG. 10 is a block diagram of a side view of an illustrative magneticfield sensor that can be like the magnetic field sensor of FIGS. 1 and2;

FIG. 11 is a graph showing phase shift per period of the first andsecond signals of FIG. 3 and for different quantities of the targetfeatures of FIGS. 1 and 2;

FIG. 12 is a graph showing illustrative signals generated by the firstand second one or more magnetic field sensing elements of FIGS. 1 and 2,and also rising and falling crossing-points that can be used to detectangular position of the target object when the target object rotates;

FIG. 13 is a graph showing the signals of FIG. 12, but on a wider timescale;

FIG. 14 is a block diagram showing an illustrative magnetic field sensorproximate to two target object portions, here shown to be separate, thatcan be like the magnetic field sensor and two portions of FIGS. 1 and 2,which can generate the signals of FIGS. 10 and 11, and which can have acrossing detection module and an amplitude difference module to identityan amplitude difference between the upper and lower crossings of thesignals of FIGS. 12 and 13;

FIG. 15 is a block diagram showing an illustrative amplitude differencemodule that can be used as the amplitude difference module of FIG. 14;

FIG. 16 is a graph showing a simulated relationship between risingcrossing points of the signals of FIGS. 12 and 13 and angle of a targetobject for different air gaps and for a target object in the form of agear having teeth (features) with ninety degree edges and in aback-biased arrangement;

FIG. 17 is a graph showing a simulated relationship between risingcrossing points of the signals of FIGS. 12 and 13 and angle of a targetobject for different air gaps and for a target object in the form of aring or circular magnet having poles (features);

FIG. 18 is a graph showing a first derivative of the data (at one airgap) from FIG. 16 in terms of change per period;

FIG. 19 is a graph showing two simulated relationships like therelationship of FIG. 14, but for two different pairings of the magneticfield sensing elements of FIGS. 1 and 2;

FIG. 20 is a graph showing two simulated relationships like therelationship of FIG. 18, but for two different pairings of the magneticfield sensing elements of FIGS. 1 and 2;

FIG. 21 is a block diagram showing another illustrative magnetic fieldsensor proximate to two target object portions, here shown to beseparate, that can be like the magnetic field sensor and two portions ofFIGS. 1 and 2, which can generate the signals of FIGS. 12 and 13, whichcan have a crossing detection module and an amplitude difference moduleto identity an amplitude difference between the upper and lowercrossings of the signals of FIGS. 12 and 13, and which has a positionrange detection module to switch magnetic field sensing elementsaccording to the graphs if FIGS. 19 and 20;

FIG. 22 is a pictorial showing a perspective view of another magneticfield sensor proximate to a target object, the target object havingfirst and second portions, wherein the first and second portions havedifferent numbers of target features, and wherein the magnetic fieldsensor has one or more magnetic field sensing elements disposedproximate to a junction between the first portion and second portion;

FIG. 23 is a pictorial diagram showing a side view of the magnetic fieldsensor and target object of FIG. 19;

FIG. 24 is a graph showing two signals that can be generated by themagnetic field sensing elements of FIG. 19;

FIG. 25 is a block diagram showing an illustrative magnetic field sensorproximate to two target object portions, here shown to be conjoined,that can be like the magnetic field sensor and two portions of FIGS. 22and 23, which can generate the signals of FIG. 24, and which can have anamplitude detection module operable to identify an amplitude of thesignals of FIG. 24;

FIG. 26 is a flow chart showing an illustrative process that can be usedby the amplitude detection module of FIG. 25;

FIG. 27 is a block diagram showing another illustrative magnetic fieldsensor proximate to two target object portions, here shown to beconjoined, that can be like the magnetic field sensor and two portionsof FIGS. 22 and 23, which can generate one of the signals of FIG. 24,and which can have an amplitude detection module operable to identify anamplitude of one of the signals of FIG. 24;

FIG. 28 is a block diagram of a side view of an illustrative magneticfield sensor that can be like the magnetic field sensor of FIGS. 22 and23; and

FIG. 29 is an isometric drawing of a flat target object having twodifferent portions, each with a different quantity of target features,and first and second substrates of magnetic field sensors according toFIGS. 1 and 2 and FIGS. 22 and 23, respectively.

DETAILED DESCRIPTION

Before describing the present invention, it should be noted thatreference is sometimes made herein to target objects having a particularshape (e.g., round). One of ordinary skill in the art will appreciate,however, that the techniques described herein are applicable to avariety of sizes and shapes, including a flat target object.

Before describing the present invention, some introductory concepts andterminology are explained.

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element may be a single element or,alternatively, may include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element may be a device made ofa type IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) andvertical Hall elements tend to have axes of sensitivity parallel to asubstrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

The terms “parallel” and” perpendicular” are used in various contextsherein. It should be understood that the terms parallel andperpendicular do not require exact perpendicularity or exactparallelism, but instead it is intended that normal manufacturingtolerances apply, which tolerances depend upon the context in which theterms are used. In some instances, the term “substantially” is used tomodify the terms “parallel” or “perpendicular.” In general, use of theterm “substantially” reflects angles that are beyond manufacturingtolerances, for example, within +/−ten degrees.

As used herein, the term “processor” is used to describe an electroniccircuit that performs a function, an operation, or a sequence ofoperations. The function, operation, or sequence of operations can behard coded into the electronic circuit or soft coded by way ofinstructions held in a memory device. A “processor” can perform thefunction, operation, or sequence of operations using digital values orusing analog signals.

In some embodiments, the “processor” can be embodied in an applicationspecific integrated circuit (ASIC), which can be an analog ASIC or adigital ASIC. In some embodiments, the “processor” can be embodied in amicroprocessor with associated program memory. In some embodiments, the“processor” can be embodied in a discrete electronic circuit, which canbe analog or digital, and which may or may not have an arithmetic logicunit (ALU).

As used herein, the term “module” can be used to describe a “processor.”However, the term “module” is used more generally to describe anycircuit that can transform an input signal into an output signal that isdifferent than the input signal.

A processor can contain internal processors or internal modules thatperform portions of the function, operation, or sequence of operationsof the processor. Similarly, a module can contain internal processors orinternal modules that perform portions of the function, operation, orsequence of operations of the module.

While electronic circuits shown in figures herein may be shown in theform of analog blocks or digital blocks, it will be understood that theanalog blocks can be replaced by digital blocks that perform the same orsimilar functions and the digital blocks can be replaced by analogblocks that perform the same or similar functions. Analog-to-digital ordigital-to-analog conversions may not be explicitly shown in thefigures, but should be understood.

In particular, it should be understood that a so-called comparator canbe comprised of an analog comparator having a two state output signalindicative of an input signal being above or below a threshold level (orindicative of one input signal being above or below another inputsignal). However, the comparator can also be comprised of a digitalcircuit having an output signal with at least two states indicative ofan input signal being above or below a threshold level (or indicative ofone input signal being above or below another input signal),respectively, or a digital value above or below a digital thresholdvalue (or another digital value), respectively.

As used herein, the term “predetermined,” when referring to a value orsignal, is used to refer to a value or signal that is set, or fixed, inthe factory at the time of manufacture, or by external means, e.g.,programming, thereafter. As used herein, the term “determined,” whenreferring to a value or signal, is used to refer to a value or signalthat is identified by a circuit during operation, after manufacture.

As used herein, the term “amplifier” is used to describe a circuitelement with a gain greater than one, less than one, or equal to one.

As used herein, the terms “line” and “linear” are used to describeeither a straight line or a curved line. The line can be described by afunction having any order less than infinite.

While planar Hall effect elements are shown in some figures herein, inother embodiments, any type of magnetic field sensing elements can beused.

The terms “absolute position” and “absolute angle” are used to refer toa position or an angle of a target object relative of a referenceposition determined by a position of a magnetic field sensor.

Referring to FIG. 1, a magnetic field sensor 102 can sense an absoluteposition (i.e., absolute rotation angle) of a target object 106. Thetarget object 106 has a first portion 106 a having a first quantity oftarget features, e.g., target features 106 aa, 106 ab, and a secondportion 106 b having a second quantity of target features, e.g., targetfeatures 106 ba, 106 bb, different than the first quantity. The firstand second portions 106 a, 106 b can be mechanically fixed together. Thetarget object 106, including the first and second portions 106 a, 106 b,is capable of a movement relative to the magnetic field sensor 102. Themagnetic field sensor 102 can include a first one or more magnetic fieldsensing elements 104 a disposed proximate to the first portion 106 a.The first one or more magnetic field sensing elements 104 a can beoperable to generate a first magnetic field signal responsive to themovement (e.g., rotation) of the first portion 106 a. The magnetic fieldsensor 102 can also include a second one or more magnetic field sensingelements 104 b disposed proximate to the second portion 106 b. Thesecond one or more magnetic field sensing elements 104 b can be operableto generate a second magnetic field signal responsive to the movement ofthe second portion 106 b. The magnetic field sensor 102 can also includea position detection module coupled to use the first and second magneticfield signals to generate a position value indicative of the absoluteposition, and an output format module coupled to receive the positionvalue and to generate an output signal from the magnetic field sensorindicative of the absolute position. The position detection module andthe output format module are described in conjunction with figuresbelow.

Examples described herein use target objects for which the quantities offeatures on the first and second portions of the target object differ byone feature. However, in other embodiments, the difference can begreater, for example, one, two, three, four, five, or more than fivefeatures.

Embodiments described herein use target objects having first and secondtarget object portions that rotate or move in the same direction.

In some embodiments, some of the target features, e.g., 106 aa, 106 ba,are teeth of a respective ferromagnetic gear portion and other targetfeatures, e.g., 106 ab, 106 bb, are valleys. These embodiments caninclude a permanent magnet (see, e.g., FIG. 10) disposed within orproximate to the magnetic field sensor 102 in a so-called “back-biased”arrangement. In a back-biased arrangement, the magnetic field sensor 102experiences changes of magnetic field generated by the permanent magnetas the gear teeth and valleys pass by the magnetic field sensor 102.

In other embodiments, some of the target features, e.g., 106 aa, 106 baare north magnetic poles of a respective ring magnet portion and othertarget features, e.g., 106 ab, 106 bb, are south magnetic poles. Theseembodiments have no back-biased magnet.

Referring now to FIG. 2, in which like element so FIG. 1 are shownhaving like reference designations, the magnetic field sensor 102 isagain shown proximate to the target object 106. Here, the first one ormore magnetic field sensing elements 104 a can include three magneticfield sensing elements S1, S2, S3, and the second one or more magneticfield sensing elements 104 b can include three magnetic field sensingelements S4, S5, S6.

Electronic circuits that use the first one or more magnetic fieldsensing elements 104 a and the second one or more magnetic field sensingelements 104 b are shown in figures below.

Referring now to FIG. 3, a graph 300 has a horizontal axis with a scalein units of time in arbitrary units and a vertical axis with a scale inunits of differential magnetic field in arbitrary units. In someembodiments, the differential field can be identified by a difference ofsignals from the magnetic field sensing elements S1, S2, S3 of FIG. 2and a difference of signals from the magnetic field sensing elements S4,S4, S6 of FIG. 2. In other embodiments described below, differentialarrangements are not used and the magnetic field sensor can use only twoof the magnetic field sensing elements S1, S2, or S3 and S4, S5, or S6,taken individually.

A signal 302 is indicative of the difference of signals from themagnetic field sensing elements S1, S2, S3 of FIG. 2 and a signal 304 isindicative of the difference of signals from the magnetic field sensingelements S4, S5, S6 of FIG. 2 as the target object 106 spins or rotates.For example, referring briefly to FIGS. 1 and 2, signal 302 can beindicative of a difference S1-S2 and signal 304 can be indicative of adifference S4-S5. However, other differences are possible.

Since the magnetic field sensing elements S1, S2, S3 are proximate tothe first portion 106 a of the target object 106 and the magnetic fieldsensing elements S4, S5, S6 are proximate to the second portion 106 b ofthe target object 106, the signals 302, 304 can have a phase differencethat changes with rotation of the target object.

The phase difference of the signals 302, 304 can be determined in avariety of ways. In some embodiments, the phase difference can bedetermined using a threshold value 306 and comparing the first andsecond signal 302, 304 to the threshold value 306. Differences of timeswhen the first signal 302 and the second signal 304 cross the thresholdvalue 306 are identified as a shift(1) and a shift(2), each of which, intime (e.g., as a percentage of a period of one of the signals 302, 304),is indicative of a phase difference between the first and second signals302, 304, wherein the phase difference changes with cycle of the firstand second signals 302, 304. Period1 and Period2 are different periods.

The above arrangement is described more fully below in conjunction withFIGS. 4 and 5. Other arrangements that can identify the phase differencebetween the first and second signals 302, 304 are described below inconjunction with FIGS. 6 and 7.

Referring now to FIG. 4, an illustrative magnetic field sensor 400 canbe disposed proximate to a first portion 404 a of a target object and asecond portion 404 b of a target object. The first and second portions404 a, 404 b of the target object can be the same as or similar to thefirst and second portions 106 a, 106 b of the target object 106 of FIGS.1 and 2. While the first and second portions 404 a, 404 b shown to beseparate, it should be understood that the first and second portions 404a, 404 b are shown as being mechanically separate merely for clarity inreference to the magnetic field sensor 400.

The magnetic field sensor 400 can include a first one or more magneticfield sensing elements 406 a, 406 b, 406 c disposed proximate to thefirst portion 404 a of the target object. The magnetic field sensor 400can also include a second one or more magnetic field sensing elements440 a, 440 b, 440 c disposed proximate to the second portion 404 b ofthe target object. The first one or more magnetic field sensing elements406 a, 406 b, 406 c can be the same as or similar to the first one ormore magnetic field sensing elements 104 a of FIGS. 1 and 2. The secondone or more magnetic field sensing elements 440 a, 440 b, 440 c can bethe same as or similar to the second one or more magnetic field sensingelements 104 b of FIGS. 1 and 2.

Magnetic field sensing elements 406 a, 406 c can be coupled in adifferential arrangement to input nodes of an amplifier 408 to generatean amplified signal 408 a.

An automatic gain control and automatic offset control circuit 410 canbe coupled to the amplified signal 408 a and can generate a controlledsignal 410 a, also indicated with a designation A.

A threshold generator circuit 416 can be coupled to the controlledsignal 410 a and can generate a threshold signal 416 a.

The controlled signal 410 a and the threshold signal 416 a can becoupled to input nodes of comparator 412 to generate a comparison signal412 a, also indicated with a designation A′. In some embodiments, thecomparison signal 412 a is a two state signal with high states and lowstates. The comparison signal 412 a can also be referred to as a speedsignal for which a rate of transitions is indicative of a speed ofrotation of the first and second portions 404 a, 404 b of the targetobject.

Generation of threshold signals is briefly described above. Let itsuffice here to say that the threshold generator 416 can be operable toidentify one or more threshold values between a positive peak and anegative peak of the controlled signal 410 a. For example, in someembodiments, the threshold generator 416 can sequentially identify afirst threshold value that is about sixty percent of a range between thepositive peak and the negative peak of the controlled signal 410 a, anda second threshold value that is about forty percent of the rangebetween the positive peak and the negative peak of the controlled signal410 a. Thus, the comparison signal 412 a can have transitions of statewhen the controlled signal 410 a crosses upward past the first thresholdvalue and crosses downward past the second threshold value, back andforth.

Magnetic field sensing elements 406 b, 406 c can be coupled in anotherdifferential arrangement to input nodes of an amplifier 422 to generatean amplified signal 422 a.

The amplified signal 408 a and the amplified signal 422 a can both havecharacteristics comparable to the signal 302 of FIG. 3.

An automatic gain control and automatic offset control circuit 424 canbe coupled to the amplified signal 422 a and can generate a controlledsignal 424 a, also indicated with a designation B.

A threshold generator circuit 428 can be coupled to the controlledsignal 424 a and can generate a threshold signal 428 a.

The controlled signal 424 a and the threshold signal 428 a can becoupled to input nodes of a comparator 426 to generate a comparisonsignal 426 a, also indicated with a designation B′. In some embodiments,the comparison signal 426 a is a two state signal with high states andlow states.

Magnetic field sensing elements 440 a, 440 c can be coupled in adifferential arrangement to input nodes of an amplifier 442 to generatean amplified signal 442 a. An automatic gain control and automaticoffset control circuit 446 can be coupled to the amplified signal 442 aand can generate a controlled signal 446 a, also indicated with adesignation C.

A threshold generator circuit 450 can be coupled to the controlledsignal 446 a and can generate a threshold signal 450 a.

The controlled signal 446 a and the threshold signal 450 a can becoupled to input nodes of comparator 448 to generate a comparison signal448 a, also indicated with a designation C′. In some embodiments, thecomparison signal 448 a is a two state signal with high states and lowstates.

Magnetic field sensing elements 440 b, 440 c can be coupled in anotherdifferential arrangement to input nodes of an amplifier 452 to generatean amplified signal 452 a.

The amplified signal 442 a and the amplified signal 452 a can both havecharacteristics comparable to the signal 304 of FIG. 3, having atime/phase shift relative to the signals 408 a, 422 a that changes withrotation angle of the target object.

An automatic gain control and automatic offset control circuit 454 canbe coupled to the amplified signal 452 a and can generate a controlledsignal 454 a, also indicated with a designation D.

A threshold generator circuit 458 can be coupled to the controlledsignal 454 a and can generate a threshold signal 458 a.

The controlled signal 454 a and the threshold signal 458 a can becoupled to input nodes of a comparator 456 to generate a comparisonsignal 456 a, also indicated with a designation D′. In some embodiments,the comparison signal 456 a is a two state signal with high states andlow states.

The magnetic field sensor 400 can also include a position detectionmodule 428. The position detection module 428 can include a 4:2multiplexer 430 coupled to the signals A and B (or alternatively, thesignals A′ and B′). The 4:2 multiplexer 430 can also be coupled to thesignals C and D (or alternatively, the signals C′ and D′).

The 4:2 multiplexer 430 is operable to generate two signals 430 a, 430 bin one or more of the following combinations:

If signals A, B, C, D are used, then:

A, C,

B, D,

B, C, or

A, D

If signals A′, B′, C′, D′ are used, then:

A′, C′,

B′, D′,

B′, C′, or

A′, D′.

The two signals 430 a, 430 b can be selected in accordance with amultiplexer control signal 436 a.

The two signals 430 a, 430 b are coupled to a phase difference module432 operable to identify a phase difference between the two signals 430a, 430 b and operable to generate a phase difference signal 432 a.Circuits described in figures below describe arrangements that can beused as the phase difference module 432.

A position decoder module 434 can be coupled to the phase differencesignal 432 a and can generate a position signal 434 a indicative of aposition (e.g., a rotation angle) of the target object 404 a, 404 b. Tothis end, in some embodiments, the position decoder module 434 can be anon-volatile memory device that can act as a decoder between the phasedifference signal 432 a and the position signal 434 a.

An element selection circuit 436 can be coupled to an element selectionsignal 438 from outside of the magnetic field sensor 400 and can beoperable to generate the multiplexer control signal 436 a to controlwhich ones of the above-listed signals are used.

An output format module 420 can be coupled to one or more of theposition signal 434 a, the speed signal 412 a, or the direction signal418 a. The output format module 420 can be operable to generate aformatted output signal 420 a indicative of one or more of a position, aspeed, or a direction of movement of the portions 404 a, 404 b of thetarget object.

The formatted output signal 420 a can be in any one of a variety offormats, including, but not limited to, SPI (serial peripheralinterface), PWM (pulse width modulation), I2C, and SENT (Single EdgeNibble Transmission).

In some embodiments, position information carried by the formattedsignal 420 a is present only during a time period proximate to a powerup of the magnetic field sensor. In other embodiments, positioninformation carried by the formatted signal 420 a is present only duringa time period proximate to first movement of the portions 404 a, 404 bof the target object after they have stopped. Thereafter, the formattedsignal can be indicative of only one or more of the speed or thedirection of movement of the portions 404 a, 404 b of the target object.

Operation of the magnetic field sensor is described in figures below.However, let it suffice here to say that a phase difference between theabove-listed two signals 430 a, 430 b is indicative of an absoluterotation angle of the target object 404 a, 404 b.

In some embodiments, some of the elements of the magnetic field sensor400 can be omitted. For example, in some embodiments, there is noselection of the two signals 430 a, 430 b, and instead, the two signal430 a, 430 b are predetermined and hard wired, in which case, the 4:2multiplexer 430, the element selection circuit 436, and circuits thatgenerate unused ones of the signals A, B, C, D, A′, B′, C′, D′ can beomitted.

In some embodiments, the AGC/AOA circuits 410, 424, 446, 454 can beomitted and similar functions can instead be embedded within othermodules, for example, within the phase difference module 432.

In some embodiments, the first one or more magnetic field sensingelements 406 a, 406 b, 406 c can consist of only two magnetic fieldsensing elements 406 a, 406 b and the second one or more magnetic fieldsensing elements 440 a, 440 b, 440 c can consist of only two magneticfield sensing elements 440 a, 440 b. In some embodiments, the first oneor more magnetic field sensing elements 406 a, 406 b, 406 c can consistof only one magnetic field sensing element 406 a and the second one ormore magnetic field sensing elements 440 a, 440 b, 440 c can consist ofonly one magnetic field sensing element 440 a.

Referring now to FIG. 5, an illustrative phase difference module 500 canbe the same as or similar to the phase difference module 432 of FIG. 4.It will be understood that a phase difference between two signals can bedetermined by a time difference between the two signals.

The phase difference module can be coupled to the two signals 430 a, 430b of FIG. 4, which can be any of the two signals listed above.

If the signals A, B, C, D are used, then the phase difference module 500can be coupled to the signals A or B and the signals C or D of FIG. 4.

A threshold generator 504 can identify a threshold associated with thesignal A or B and can generate a threshold signal 504 a. A thresholdgenerator 512 can identify a threshold associated with the signal C or Dand can generate a threshold signal 512 a. In some embodiments, thethreshold generators 504, 512 are operable to identify singlethresholds, for example, at eighty, seventy, sixty, or fifty percent ofas peak-to-peak range of respective input signals A, B, C, or D.

A comparator 502 can be coupled to the signal A or B and the thresholdsignal 504 a and can generate a two-state comparison signal 502 a. Acomparator 510 can be coupled to the signal C or D and the thresholdsignal 512 a and can generate a two-state comparison signal 510 a.

A start/stop counter 506 can be coupled to the comparison signal 502 aat a start input node and can be coupled to receive the comparisonsignal 510 a at a stop input node, both nodes responsive topredetermined direction of state transitions. The start/stop counter 506can generate a count signal 506 a received at latches 508 operable totemporarily store the count signal 506 a to generate a latched countsignal 508 a.

An oscillator 514 can generate a clock signal 514 a received at a clockinput node of the start/stop counter 506.

A time delay circuit 516 can be coupled to the comparison signal 510 aand can generate a time delayed signal coupled to a reset input node ofthe start/stop counter 506 to reset the start/stop counter 506 shortlyafter the start/stop counter 506 is stopped by the comparison signal 510a.

The latches 508 a can be latched upon a state of the comparison signal510 a being received at a latch input node of the latches 508 a.

Count values from the latches 508 are indicative of a phase between thetwo signals A or B and C or D, in arbitrary units.

In an alternative embodiment, the signals A or B and C or D are notreceived by the phase difference module 500. In these embodiments, thesignals A′ or B′ and C′ or D′ of FIG. 4 are received by the phasedifference module 500. The signals A′, B′, C′, and D′ are alreadytwo-state signals. The signal A′ or B′ can be received at the start nodeof the start/stop counter 506 instead of the comparison signal 502 a.The signal C′ or D′ can be received at the stop node of the start/stopcounter 506 instead of the comparison signal 502 a.

The phase difference module 500 determines a phase difference betweentwo signals by measuring a time difference between the two signals.Essentially, the phase difference module 500 can identify timedifferences between points on the signals 302, 304 of FIG. 3 where theycross the threshold value 306. Embodiments described in conjunction withFIGS. 6 and 7 use other circuits to determine a phase difference betweentwo signals.

Referring now to FIG. 6, another illustrative phase difference module600 can be the same as or similar to the phase difference module 432 ofFIG. 4. The phase difference module 600 can include a correlation module602 coupled to the signals A or B and the signals C or D of FIG. 4.Correlation is a technique that can identify a phase difference betweentwo signals. Thus, the correlation module 602 can generate a phasesignal 602 a.

Referring now to FIG. 7, another illustrative phase difference module700 can be the same as or similar to the phase difference module 432 ofFIG. 4. The phase difference module 700 can include a phase locked loop(PLL) module 702 coupled to the signals A or B and the signals C or D ofFIG. 4. A phase locked loop can identify a phase difference between twosignals. Thus, the correlation module 702 can generate a phase signal702 a.

Referring now to FIG. 8, in which like elements of FIG. 4 are shownhaving like reference designations, a magnetic field sensor 800 can bedisposed proximate to the first and second portions 404 a, 404 b of thetarget object. The magnetic field sensor 800 is a reduced version of themagnetic field sensor 400 of FIG. 4, and operates in substantially thesame way.

A magnetic field sensing element 804 can be operable to generate amagnetic field signal 804 a coupled to an amplifier 806. The amplifier806 can be operable to generate an amplified signal 806 a.

An AGC/AOA module 808 can be coupled to the amplified signal 806 a andcan generate a controlled signal 808 a, also indicated with adesignation A.

A threshold generator 812 can be coupled to the controlled signal 808 aand can generate a threshold signal 812 a.

The controlled signal 808 a and the threshold signal 812 a can becoupled to input nodes of comparator 810 to generate a comparison signal810 a, also indicated with a designation A′. In some embodiments, thecomparison signal 810 a is a two state signal with high states and lowstates. The comparison signal 810 a can also be referred to as a speedsignal for which a rate of transitions is indicative of a speed ofrotation of the first and second portions 404 a, 404 b of the targetobject.

A magnetic field sensing element 816 can be operable to generate amagnetic field signal 816 a coupled to an amplifier 818. The amplifier818 can be operable to generate an amplified signal 818 a.

An AGC/AOA module 820 can be coupled to the amplified signal 8018 a andcan generate a controlled signal 820 a, also indicated with adesignation C

A threshold generator 824 can be coupled to the controlled signal 820 aa and can generate a threshold signal 812 a.

The controlled signal 820 a and the threshold signal 824 a can becoupled to input nodes of comparator 822 to generate a comparison signal822 a, also indicated with a designation C′. In some embodiments, thecomparison signal 822 a is a two state signal with high states and lowstates.

A phase difference module 828 can be coupled to the signals A and C orA′ and C′. The phase difference module can be the same as or similar tothe phase difference module 432 of FIG. 4. Because the signals A or Cand A′ or C′ can be statically coupled to the phase difference module828, the phase difference module need not be preceded by the multiplexer430 of FIG. 4. However, in other embodiments, a multiplexer can be addedto selected between the signals A or A′ and C or C′.

The phase difference module can be operable to generate a phase signal432 a indicative of a phase difference between the signals A or A′ and Cor C′.

A position decoder module 830 can be coupled to the phase signal 828 a aand can decode the phase signal 828 a to produce position signal 830 asimilar to the position signal 432 a of FIG. 4.

Referring now to FIG. 9, in which like elements of FIG. 4 are shownhaving like reference designations, magnetic field sensor 900 can employother techniques to generate the speed and direction signals of FIG. 4.The magnetic field sensor 900 can have a position detection module thatcan be similar to the position detection module of FIG. 4, and that cangenerate a position signal 930 a similar to the positions signal 434 aof FIG. 4 indicative of a position (e.g., angle) of the portions 404 a,404 b of the target object. It should be understood that, from theposition signal 930 a, both speed of movement and direction of themovement of the portions 404 a, 404 b of the target object can becalculated. To this end, some of the circuits of FIG. 4 can be omittedas shown in FIG. 9.

A speed detection module 934 can be coupled to the position signal 930 aand can generate a speed signal 934 a indicative of a speed or rate ofmovement of the portions 4040 a, 404 b of the target object.

A direction detection module 932 can be coupled to the position signal930 a and can generate a direction signal 932 a indicative of adirection of the movement of the portions 4040 a, 404 b of the targetobject.

An element selection module 936 and multiplexer control signal 936 a canbe similar to the element selection module 436 and multiplexer controlsignal 436 a of FIG. 4.

An output format module 920 and formatted signal 920 a can be the sameas or similar to the output format module and formatted signal 420 a ofFIG. 4.

Referring now to FIG. 10, a magnetic field sensor 1000 can beillustrative of a mechanical arrangement of any of the magnetic fieldsensors of figures above.

The magnetic field sensor 1000 can include a first semiconductorsubstrate 1002 upon which can be disposed the first one or more magneticfield sensing elements 406 a, 406 b, 406 c of FIG. 4 of 804 of FIG. 8.The magnetic field sensor 1000 can also include a second semiconductorsubstrate 1004 upon which can be disposed the second one or moremagnetic field sensing elements 440 a, 440 b, 440 c of FIG. 4 or 816 ofFIG. 8. With the two substrates, the groups of magnetic field sensingelements can be more widely separated than would otherwise be possibleif all of the magnetic field sensing elements were disposed on a singlesemiconductor substrate.

In some embodiments, other elements of the magnetic field sensor 400 ofFIG. 4 or 800 of FIG. 8 can be disbursed among the first and secondsemiconductor substrates. However, in another embodiment, some of theother elements can be disposed upon an optional third semiconductorsubstrate 1006.

The semiconductor substrates 1002, 1004, 1006 can be coupled to a basesubstrate 1008, which can be comprised of a semiconductor or insulator(e.g., ceramic) material. The coupling to the base substrate can be madeby solder balls, e.g., 1010, or the like. Interconnecting traces uponthe base substrate 1008 can make interconnections between thesemiconductor substrates 1002, 1004, 1006.

The base substrate 1008 can be coupled to a base plate 1012 a of a leadframe 1012 to make connection to leads, e.g., 1012 b, of the lead frame1012. In some embodiments, the leads, e.g., 1012 b, can be formed into asurface mount configuration.

In back biased arrangements used to sense a movement of a ferromagnetictarget object, a permanent magnet 1016 can be disposed proximate to thesubstrates 1002, 1004, 1006. In other embodiments used to sense a ringmagnet, the permanent magnet 1016 can be omitted.

A solid molded enclosure 1018 can surround parts of the magnetic fieldsensor 1000 as shown.

In some alternate embodiments, the magnetic field sensors describedabove are disposed entirely upon one substrate.

Referring now to FIG. 11, a graph 1100 has a horizontal axis with ascale in units of rotation speed of the portions 404 a, 404 b of thetarget object of FIG. 4 in unit of revolutions per minute. The graph1100 has a vertical axis with a scale in units of time shift per periodin units of seconds. The time shift is essentially the shift identifiedin FIG. 3, where the shift changes with each cycle of the signals 302,304.

A line 1102 is indicative of one of the portions, e.g., 404 a of FIG. 4,of the target object having twenty teeth and the other portion havingtwenty-one teeth. A line 1104 is indicative of one of the portions,e.g., 404 a of FIG. 4, of the target object having one hundred teeth andthe other portion having one hundred one teeth. Other lines on the graph1100 are at intervals of twenty teeth.

From the graph 1100 it can be seen that the shift per period is less forhigher rotation speeds. Also, the shift per period is less for targetobjects with greater numbers of teeth (or poles). For embodiments usingthe time shift from FIG. 3 to determine absolute angle, a timeresolution of the magnetic field sensor can limit the maximum allowablerotation speed at which absolute angles can be reliably determined. Thegraph 1100 serves to predict the maximum allowable rotation speed for anumber of target combinations. For example, from the graph 1100, for amagnetic field sensor that can resolve time shifts greater than or equalto one hundred microseconds, assuming a pair of targets with twenty andtwenty one features (line 1102), the maximum target speed would beapproximately two thousand revolutions per minute.

Referring now to FIG. 12, a graph 1200 has a horizontal axis with ascale in units of absolute angle of the target object 106 of FIG. 1,having two target object portions, in units of degrees, and a verticalaxis with a scale in units of differential magnetic field in normalizedarbitrary units related to that which would be experienced by twomagnetic field sensing elements taken differentially. In someembodiments, the differential field can be identified by a difference ofsignals from the magnetic field sensing elements S1, S2, S3 of FIG. 2,e.g., S1-S2, which is like signal 1202, and a difference of signals fromthe magnetic field sensing elements S4, S5, S6 of FIG. 2, e.g., S4-S5,which is like the signal 1204.

The graph 1200 shows first and second signals 1202, 1204 that aresimilar to the signals 302, 304 of FIG. 3. The absolute angle of thehorizontal axis is similar to the time on the horizontal axis of FIG. 3.Here, unlike FIG. 3, the signals 1202, 1204 are not compared to athreshold (e.g., 306 of FIG. 3), but instead, proximate (in time)crossings (e.g., 1206, 1208, respectively) of the first and secondsignals 1202, 1204 are identified.

Like the time shifts shown on FIG. 3, which change depending uponrotation angle of the target object, here, it should be apparent thatvertical locations of the crossings (e.g., 1206, 1208) change withrotation angle of the target object. In order to uniquely identify allabsolute angles of the target, the magnetic field sensor can distinguishbetween crossings at which the slope of signal 1204 is positive andcrossings at which the slope of signal 1204 is negative at the time ofeach crossing. Magnetic field sensors described below in conjunctionwith FIGS. 14 and 21 use this behavior. Magnetic field sensors describedherein can use one, the other, or both the crossings at the positiveslope of the signals 1204 and crossings at the negative slope of thesignal 1204.

Referring now to FIG. 13, a graph 1300 has the same axes as those of thegraph 1200 of FIG. 12. Here, however, the horizontal axis has a widerangle scale. Points 1302 are indicative of signal crossings for whichthe slope of signal 1204 is positive, while points 1304 are indicativeof signal crossings for which the slope of signal 1204 is negative.These points are like those of FIG. 12, but are visible throughout arange of angular rotations of the target object 106 of FIGS. 1 and 2. Itshould be apparent that some embodiments can use either the crossings1302 at the positive slope of the signal 1204 or crossings 1304 at thenegative slope of the signal 1204. Either can uniquely identify theabsolute angle.

Other embodiments can use a difference between proximate crossings, e.g.points 1206, 1208 of FIG. 12, in order to determine the absoluteposition of the target. In this case, it is both the difference betweenproximate crossings and the sign of the difference that are indicativeof the angle of rotation. It should be apparent that these embodimentscan use both the crossings at the positive slope of the signal 1204 andcrossings at the negative slope of the signal 1204.

Referring now to FIG. 14, in which like elements of FIG. 4 have likereference designations, the position detection mode 428 of FIG. 4 isreplaced by a position detection module 1402 that makes use of thesignal crossing difference of FIGS. 12 and 13.

The position detection module can include a 4:2 multiplexer 1404 similarto the 4:2 multiplexer 430 of FIG. 4. However, only the signal A or Band C or D are received by and used by the 4:2 multiplexer 1404.

The 4:2 multiplexer 1404 can select and generate two signals (see, e.g.,signal 1202, 1204 of FIG. 12) from the group of two signals:

A,C

B, D

A, D

B, C

The selection is determined in accordance with a multiplexer controlsignal 436 a.

The selected two signals can be coupled to a crossing detection module1406 operable to detect some of or all of the crossings of the twosignals received by the crossing detection module. An illustrativecrossing detection module is described below in conjunction with FIG.15. The crossing detection module 1406 can be operable to generate acrossing signal 1406 a indicative of the detected crossings of the twosignals.

Optionally, (shown as phantom lines) an amplitude difference module 1408can identify a difference of amplitudes between proximate crossings ofthe crossing signal 1406 a. The amplitude difference module 1408 cangenerate a difference signal 1408 a indicative of the difference ofamplitudes, which, as identified in conjunction with FIGS. 12 and 13, isindicative of an angle of rotation of the first and second portions 404a, 404 b of the target object.

A position decoder module 1210 can be coupled to the crossing signal1406 a (or optionally, to the difference signal 1408 a) and can beoperable to generate a position signal 1410 a indicative of a position(e.g., angular position) of the target object.

Output format module 420 can generate a formatted signal that can be thesame as or similar to the formatted signal 420 a of FIG. 4.

Referring now to FIG. 15, an illustrative crossing detection module 1500can include a comparator 1502 to generate a crossing signal 1502 aindicative of crossings of the signals A or B and C or D. The crossingsignal 1502 a can be the same as or similar to the crossing signal 1406a of FIG. 14.

Referring now to FIGS. 16 and 17, graphs 1600 and 1700 each include ahorizontal axis with a scale in units of rotation angle of the portions404 a, 404 b of the target object of FIG. 14 in degrees and each includea vertical axis with a scale in units of normalized differentialmagnetic field at which crossing points of two signals occur (e.g.,points 1304 in FIG. 13). Points 1602 are indicative of only one set ofcrossings of the signals 1202 and 1204 of FIG. 12, e.g., crossings 1304of FIG. 13. The other set of crossings, e.g., 1302 of FIG. 13 is omittedfor clarity.

In some embodiments, a first signal is generated by a difference ofsignals from the magnetic field sensing elements S1, S2, S3 of FIG. 2,e.g., S1-S2, which is like signal 1202, and a second signal crossing thefirst signal is generated by a difference of signals from the magneticfield sensing elements S4, S5, S6 of FIG. 2, e.g., S4-S5.

A plurality of curves 1602 on the graph 1600 is indicative of aback-biased arrangement for sensing rotation of a ferromagnetic gearhaving teeth with ninety degree corners, for different air gaps betweenthe magnetic field sensor 1400 of FIG. 14 and the target object, the airgaps spanning between 0.5 mm and 3.0 mm in increments of 0.5 mm. Thedata in FIG. 16 were simulated assuming a pair of targets with sixty andsixty-one teeth.

Similarly, a plurality of curves 1702 on the graph 1700 is indicative ofa non back-biased arrangement for sensing rotation of a ring or circularmagnet having north and south poles around a circumference of the ringor circular magnet, for different air gaps between the magnetic fieldsensor 1400 of FIG. 14 and the target object, the air gaps spanningbetween 0.5 mm and 3.0 mm in increments of 0.5 mm. The data in FIG. 16were simulated assuming a pair of ring-magnet targets with sixty andsixty-one pole pairs.

An illustrative installed unit-to-unit tolerance for the air gap isabout +/−0.5 mm.

For both of the graphs 1600, 1700 it should be apparent that thevariation of crossing points with rotation angle may not be straightline linear and may change depending upon air gap. Circuits andtechniques described below in conjunction with FIGS. 19, 20, and 21 canmitigate this variation.

Referring now to FIG. 18, a graph 1800 has a horizontal axis with ascale in units of rotation angle in degrees of the portions 404 a, 404 bof the target object described above in conjunction with FIG. 14. Thegraph 1800 also has a vertical axis with a scale in units of crossingpoint change per tooth-valley period for one set of crossings, e.g.,crossings 1304 of FIG. 13. Points 1802 are indicative of rates of changeof the one set of crossings of the two signals 1202, 1204 of FIG. 12,e.g., crossings 1304 of FIG. 13.

Referring briefly to FIG. 13, for two target object portions, e.g., 404a, 404 b of FIG. 14, that differ by one tooth or one pole pair, acrossing point change per period of curve 1304 is highest near onehundred eighty degrees of rotation of the target object and lowest forrotation angles near zero and three hundred sixty degrees of rotation.

A limiting factor for accurate determination of the absolute angle inthis embodiment is the capability of the magnetic field sensor toresolve the differential field at which each crossing point occurs. Thisis the most difficult for rotation angles near zero and three hundredsixty degrees of rotation, where the crossing point change per period issmall, as shown in FIG. 18.

Referring now to FIG. 19, a graph 1900, which is like the graph 1600 ofFIG. 16, includes a horizontal axis with a scale in units of rotationangle of the portions 404 a, 404 b of the target object of FIG. 14 indegrees, and a vertical axis with a scale in units of differentialmagnetic field crossing points (see FIG. 16 for an explanation of thevertical axis).

With regard to accuracy deficiencies at some rotation angles describedabove in conjunction with FIG. 18, relatively high sensitivity can bemaintained at all rotation angles if a strategy is adopted usingdifferent pairs of sensing elements in FIG. 2 at different rotationangles of the target object, e.g. S3-S2 crossing S5-S4 (1902 a and 1902b) at some rotation angles, and, S2-S1 crossing S6-S5 (1904 a and 1904b) at other rotation angles.

This strategy of using offset pairs of sensing elements shifts theabsolute angle at which the maximum slope of the simulated data in FIG.19 occurs away from one hundred eighty degrees when compared to thesimulations in FIGS. 16-17.

FIG. 20 is similar to FIG. 18. A set of crossing point changes pertooth-valley period 2002 shows slopes of the set of points 1902 a, 1902b of FIG. 19. A set of crossing point changes per second 2004 showsslopes of the set of points 1904 a, 1904 b of FIG. 19.

It is desirable to maintain a high rate of change of the crossings ofthe two signals to maximize angle sensitivity. Thus, for example, forrotation angles of the target object between about zero and one hundredeighty degrees, the set of points 2002 can be used according tocrossings generated by S3-S2 crossing S5-S4 (see FIGS. 1 and 2), and forangles of the target object between about one hundred eighty degrees andthree hundred sixty degrees, the set of points 2004 can be usedaccording to crossings generated by S2-S1 crossing S6-S5.

Referring now to FIG. 21, in which like elements of FIGS. 4 and 14 areshown having like reference designations, a magnetic field sensor 2100is like the magnetic field sensor 1400 of FIG. 14, except that theelement selection circuit 436 of FIG. 14 is replaced by a position rangedetection circuit 2102 that can generate a multiplexer control signal2102 a that can change connections of the 4:2 multiplexer 1404 during arotation of the portions 404 a, 404 b of the target object. In someembodiments, the magnetic field sensor 2100 can control the 4:2multiplexer 1404 to use signals A and C during a first selected onehundred eighty degrees of rotation of the target object and to usesignals B and D during a second selected one hundred eighty degrees ofrotation of the target object. Other signal combinations are alsopossible.

The position decoder module 1410 of FIG. 14 can also be replaced by aposition decoder module 2101 that can account for the phase shift of thecrossing signals depicted in FIGS. 19 and 20 in accordance withdifferent signals selected by the 4:2 multiplexer 1404.

Referring now to FIG. 22, a magnetic field sensor 2204 can sense anabsolute position of a target object 2202. The target object 2202 has afirst portion 2202 a having a first quantity of target features and asecond portion 2202 b having a second quantity of target featuresdifferent than the first quantity. The first and second portions 2202 a,2202 b are proximate and mechanically fixed together. The target object2202, including the first and second portions 2202 a, 2202 b, is capableof a movement (e.g., a rotation). The magnetic field sensor 2204 caninclude one or more magnetic field sensing elements disposed proximateto a mechanical intersection 2202 c to sense both the first and secondportions 2202 a, 2202 b of the target object 2202 with the same one ormore magnetic field sensing elements. The one or more magnetic fieldsensing elements are operable to generate a first magnetic field signalresponsive to the movement of both the first and second portions 2202 a,2202 b. Described in conjunction with FIG. 25 below, the magnetic fieldsensor 2202 can include a position detection module operable to use thefirst magnetic field signal to generate a position signal (i.e., values)indicative of the absolute position and an output format module coupledto receive the position value and to generate an output signal from themagnetic field sensor indicative of the absolute position.

The magnetic field sensor 2204 is disposed at a different positionrelative to a target object 2202 than that shown in FIGS. 1 and 2.However, the target object 2202 can be the same as or similar to thetarget object 106 of FIGS. 1 and 2. Unlike the magnetic field sensor 102of FIGS. 1 and 2, the magnetic field sensor 2204 is disposed proximateto the junction 2202 c between first and second portions 2202 a, 220 bof the target object 2202.

Referring now to FIG. 23, in which like elements of FIG. 22 are shownhaving like reference designations, the magnetic field sensor 2204 isdisposed proximate to a junction 2202 c between first and secondportions 2202 a, 2200 b of the target object 2202. In this view, it canbe seen that, at some rotations of the target object, valleys of thefirst portion 2202 a of the target object 2202 are proximate to valleysof the second portion 2202 b, and at other rotations of the targetobject, valleys of the first portion 2202 a are proximate to teeth ofthe second portion 2202 b.

The magnetic field sensor 2204 can experience influence from the firstand second portions 2202 a, 2202 b together at the same time.

While the target object 2202 is shown as a gear having teeth andvalleys, in other embodiments, a ring or circular magnet can be usedwith alternating north and south poles around its circumference.

Referring now to FIG. 24, a graph 2400 has a horizontal axis with ascale in units of rotation angle of the target object 2202 of FIGS. 22and 23. The graph 2400 also has a vertical axis with a scale in units ofdifferential magnetic field in Gauss experienced by the magnetic fieldsensor 2204 of FIGS. 1 and 2.

The graph 2400 has two signals 2402, 2404. The two signals are signalsgenerated within the magnetic field sensor 2204 as the target objectrotates. At some rotations of the target object the magnetic fieldsensor 2204 is proximate to like features of the two portions 2202 a,2202 b of the target object 2200, e.g., teeth to north poles. At otherrotations, the magnetic field sensor is proximate to opposing features,e.g., a tooth and a valley or a north pole and south pole. An amplitudeof one of or both of the signals 2402, 2404 can be detected by amagnetic field sensor 25 described below.

Referring now to FIG. 25, in which like elements of FIG. 4 are shownhaving like reference designations, a magnetic field sensor 2500 can bedisposed proximate to the target object 2202 of FIGS. 22 and 23.

The magnetic field senor 2500 can generate the amplified signals 408 a,422 a of FIG. 4, also identified as A″ and B″, similar to signals A andB of FIG. 4. The signals A″ and B″ can be received by thespeed/direction module 414 of FIG. 4 to generate the speed signal 412 aand the direction signal 418 a of FIG. 4.

A maximum peak-to-peak detection module 2502 can receive the amplifiedsignal 408 a and can identify and generate a maximum peak-to-peak value2502 a of the amplified signal 408 a determined as the target object2200 rotates.

A non-volatile memory 2504, e.g., an EEPROM, can store the maximumpeak-to-peak value 2502 a. The non-volatile memory 2504 is operable toprovide a stored maximum peak-to-peak value 2504 a, also identified as asignal E.

A maximum peak-to-peak detection module 2506 can receive the amplifiedsignal 422 a and can identify and generate a maximum peak-to-peak value2506 a of the amplified signal 422 a determined as the target object2200 rotates.

A non-volatile memory 2508, e.g., an EEPROM, can store the maximumpeak-to-peak value 2506 a. The non-volatile memory 2508 is operable toprovide a stored maximum peak-to-peak value 2508 a, also identified as asignal F.

A position detection module 2510 can include an amplitude detectionmodule 2512 coupled to at least one of the signal A″ or the signal B″and coupled to at least one of the stored maximum peak-to-peak values Eor F. The amplitude detection module 2512 can be operable to identify arelative amplitude of at least one of the signal A″ or the signal B″ inview of at least one of the stored maximum peak-to-peak values E or F.The relative amplitude can be indicative of a rotation angle of thetarget object. See also FIG. 24. The amplitude detection module 2512 canbe operable to generate an amplitude signal 2512 a (i.e., one or moreamplitude values) indicative of the rotation angle.

A position decoder module 2514 can be coupled to the amplitude signal2512 a and can be operable to generate a position signal 2514 a (i.e.,position values) indicative of the rotation angle.

An output format module can be coupled to at least one of the positionsignal 2514 a, the speed signal 412 a, or the direction signal 418 a andcan be operable to generate an output signal 2516 a indicative of atleast one of the speed of rotation, the direction of rotation, and theabsolute rotation angle of the target object.

Characteristics of the output signal 2516 a can be the same as orsimilar to characteristics of the output signal 420 a of FIG. 4described above.

In some embodiments, the nonvolatile memory 2504 can be coupled to a“set E” signal 2518 to set the maximum peak-to-peak value stored in thenon-volatile memory 2504 to an initial value at start up. Similarly, insome embodiments, the nonvolatile memory 2508 can be coupled to a “setF” signal 2520 to set the maximum peak-to-peak value stored in thenon-volatile memory 2508 to an initial value at start up. Values can beupdated and stored in the nonvolatile memories 2504, 2508 during runtime of the magnetic field sensor 2500.

In some embodiments, some of the electronic circuits of the magneticfield sensor 2500 can be omitted. For example, magnetic field sensingelement 406 b, amplifier 422, maximum peak-to-peak detection module2506, and nonvolatile memory 2508 can be omitted. In this case, some ofthe speed/direction module 414 can also be omitted.

It should be appreciated that FIG. 26 shows a flowchart corresponding tothe below contemplated technique which would be implemented in amagnetic field sensor (e.g., FIGS. 25 and 27). Rectangular elements(typified by element 2602 in FIG. 26), herein denoted “processingblocks,” represent computer software instructions or groups ofinstructions. Diamond shaped elements (typified by element 2614 in FIG.26), herein denoted “decision blocks,” represent logic, or groups oflogic, which affect the execution of processing blocks.

The processing and decision blocks can represent steps performed byfunctionally equivalent circuits such as a digital signal processorcircuit or an application specific integrated circuit (ASIC). The flowdiagrams do not depict the syntax of any particular programminglanguage. Rather, the flow diagrams illustrate the functionalinformation one of ordinary skill in the art requires to fabricatecircuits or to generate computer software to perform the processingrequired of the particular apparatus. It should be noted that manyroutine program elements, such as initialization of loops and variablesand the use of temporary variables are not shown. It will be appreciatedby those of ordinary skill in the art that unless otherwise indicatedherein, the particular sequence of blocks described is illustrative onlyand can be varied without departing from the spirit of the invention.Thus, unless otherwise stated the blocks described below are unorderedmeaning that, when possible, the steps can be performed in anyconvenient or desirable order.

Referring now to FIG. 26, with reference to FIG. 25, a process 2600 canbe used in the magnetic field sensor 2500 of FIG. 25. At block 2602,initial values can be loaded into the EEPROM 2504 an/or into the EEPROM2508 via the signal 2518 and/or the signal 2520. The initial values canbe representative of a predetermined approximate maximum peak-to-peakvalue of the signals A and/or B.

At block 2604, the stored maximum peak-to-peak values can be recalledfrom the EEPROM 2504 and/or the EEPROM 2508 and conveyed to theamplitude detection module 2512.

At block 2606, the amplitude detection module can measure values ofamplitudes of the signals A″ and/or B″ as the target object 2200rotates.

At block 2608 the amplitude detection module can compare the measuredvalue(s) of the amplitude with the stored maximum peak-to-peak value(s)from the EEPROM 2604 and/or the EEPROM 2508.

At block 2618, if the measure amplitude(s) is/are not larger than thestored maximum peak-to-peak values(s) then at block 2618, the measuredamplitude(s) can be used according to FIG. 24 to determine a rotationangle of the target object 2200 by determining how much smaller themeasured amplitude value(s) is/are than the stored maximum peak-to-peakvalue(s).

At block 2620, using the position decoder module 2514, the calculatedamplitude difference(s) can be converted into a position signal (i.e.,position values) 2514 a. Then, the process 2600 can return to block2606.

On the other hand, if at block 2610, the measured amplitude values(s)is/are greater than the stored maximum peak-to-peak value(s), then it isknown that the stored maximum peak-to-peak value(s) is/are not correct.Thus, the process moves to block 2612, where the maximum peak-to-peakvalue(s) is/are updated accordingly, but not yet sent to the EEPROM(S)2504 and or 2508 for storage.

At block 2614, predetermined conditions of the magnetic field sensor canbe examined. For example, the updated maximum peak-to-peak values can beexamined to determine if they are within a predetermined range ofmaximum peak-to-peak that is proper. An improper maximum peak-to-peakvalue may be indicative of for example, a malfunctioning magnetic fieldsensing element 406 a, 406 b, 406 c. An improper maximum peak-to-peakvalue may also be indicative of only a momentary electrical or magneticnoise spike in the signals 408 a, 422 a. For another example, in someembodiments, the magnetic field sensor can include a temperature sensorand, if the temperature is not within predetermined limits, updates tothe stored maximum peak-to-peak value(s) may be stopped. For anotherexample, in some embodiments, the magnetic field sensor can perform onlyone update to the stored maximum peak-to-peak value(s) per power cycleof the magnetic field sensor.

At block 2614, if the predefined (i.e., predetermined) conditions aremet, then the process proceeds to block 2616, where maximum peak-to-peakvalue(s) stored in the EEPROMS(s) 2504 and/or 2508 is/are updated. Theprocess returns to block 2604.

On the other hand, if at block 2614, the predefined conditions are notmet, then the EEPROM(s) 2504 and/or 2508 are not updated and the processreturns to block 2606. The process can also generate a flag value toindicate that the predefined conditions were not met.

From language above should be apparent that only one of the signals A″,B″ and one of the signals E″, F″ is necessary. However, if they are allpresent, the magnetic field sensor 2500 can calculate two amplitudedifferences and two position signals (values) comparable to positionsignal 2514 a. In this case, the two position values can be combined,for example, averaged together, or they can be separately provided aspart of the formatted output signal 2516 a.

Referring now to FIG. 27, in which like elements of FIGS. 4 and 25 areshown having like reference designations, a magnetic field sensor 2700can generate and use only the signal A″ and the stored maximumpeak-to-peak value E″. This arrangement should be apparent from thediscussion above in conjunction with FIG. 26.

An output format module 2712 can be coupled to a speed signal 2171 agenerated by a speed module 2717. This arrangement is similar to thatdescribed above in conjunction with FIG. 8.

Referring now to FIG. 28, a magnetic field sensor 2800 can be like themagnetic field sensor 2500, 2700. The magnetic field sensor 2800 caninclude a single semiconductor substrate 2808 coupled with solder balls2804 or the like to a mounting plate 2806 a of a lead frame 2806.

In back-biased arrangement in which the target object 2200 is aferromagnetic object, e.g. a gear, the magnetic field sensor 2800 caninclude a permanent magnet 2808. In other back-biased arrangements, themagnet 2808 can be external to the magnetic field sensor 2800. For nonback-biased arrangements in which the target object is a ring orcircular magnet, the permanent magnet 2808 can be omitted.

A solid molded enclosure 2810 can surround parts of the magnetic fieldsensor 2800 as shown.

Referring now to FIG. 29, a flat target object 2900 can include firstand second portions 2900 a, 2900 b, each having a different quantity oftarget features (e.g., teeth and valleys or magnetic poles).

A magnetic field sensor 2902 (here showing only a substrate) can be likethe magnetic field sensor 102 of FIGS. 1 and 2, wherein a first one ormore magnetic field sensing elements is disposed proximate to the firstportion 2900 a and a second one or more magnetic field sensing elementsare disposed proximate to the second portion 2900 b.

Also shown, a different magnetic field sensor 2904 (here showing only asubstrate) can be like the magnetic field sensor 2204 of FIGS. 22 and23, wherein one or more magnetic field sensing elements is disposedproximate to a boundary between the first and second portions 2900 a,2900 b.

Movement of the target object 2900 can be parallel to a line 2906.

For back-biased arrangements, the target features of the target object2900 can be teeth and valley of a gear. For non back-biasedarrangements, the target features of the target object 2900 can be northand south poles of a multi-pole magnet.

Circuits and techniques described in conjunction with figures aboveapply equally well to the flat target object 2900 as they do to theround target objects described above.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent that other embodimentsincorporating these concepts, structures and techniques may be used.Accordingly, it is submitted that the scope of the patent should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

What is claimed is:
 1. A magnetic field sensor for sensing an absoluteposition of a target object, wherein the target object has a firstportion having a first quantity of target features and a second portionhaving a second quantity of target features different than the firstquantity, wherein the first and second portions are proximate andmechanically fixed together, wherein the target object, including thefirst and second portions, is capable of a movement, wherein themagnetic field sensor comprises: one or more magnetic field sensingelements disposed proximate to a mechanical intersection of the firstand second portions of the target object, wherein the one or moremagnetic field sensing elements are operable to generate a firstmagnetic field signal responsive to the movement of both the first andsecond portions; a position detection module operable to use the firstmagnetic field signal to generate a position value indicative of theabsolute position; and an output format module coupled to receive theposition value and to generate an output signal from the magnetic fieldsensor indicative of the absolute position.
 2. The magnetic field sensorof claim 1, wherein the absolute position of the target object comprisesan absolute angle of a rotation of the target object.
 3. The magneticfield sensor of claim 1, further comprising: a maximum peak-to-peakdetection module coupled to the first magnetic field signal and operableto generate a maximum peak-to-peak value indicative of a maximumpeak-to-peak value of the first magnetic field signal, wherein theposition detection module comprises: an amplitude detection modulecoupled to the first magnetic field signal, coupled to the maximumpeak-to-peak value, operable to measure an amplitude of the magneticfield signal, operable to compare the amplitude of the magnetic fieldsignal with the maximum peak-to-peak value and operable to generate anamplitude signal indicative of the absolute position.
 4. The magneticfield sensor of claim 2, wherein the position detection module furthercomprises: a position decoder module coupled to the amplitude signal andoperable to decode the amplitude signal to generate a position signalindicative of the absolute position.
 5. The magnetic field sensor ofclaim 3, wherein the one or more magnetic field sensing elements areoperable to generate a second magnetic field signal responsive to themovement of both the first and second portions, the magnetic fieldsensor further comprising: a speed and direction module coupled toreceive the first and second magnetic field signals and operable togenerate a speed signal indicative of a speed of the movement andoperable to generate a direction signal indicative of a direction of themovement.
 6. The magnetic field sensor of claim 3, wherein the positiondetection module comprises: an amplitude detection module operable toidentify an amplitude of the first magnetic field signal and operable togenerate an amplitude value indicate of an amplitude of the firstmagnetic field signal; and a position decoder module coupled to receivethe amplitude value, operable to relate the amplitude value to theabsolute position, and operable to generate the position value inaccordance with the amplitude value.
 7. The magnetic field sensor ofclaim 3, further comprising: a semiconductor substrate, wherein the oneor more magnetic field sensing elements, the position detection module,and the output format module are disposed upon the semiconductorsubstrate.
 8. The magnetic field sensor of claim 3, wherein the one ormore magnetic field sensing elements comprises three magnetic fieldsensing elements coupled in at least one differential arrangement in arespective at least one electronic channel.
 9. The magnetic field sensorof claim 3, wherein the one or more magnetic field sensing elementsconsist of two magnetic field sensing elements coupled in a respectivetwo electronic channels.
 10. The magnetic field sensor of claim 3,wherein the one or more magnetic field sensing elements consist of threemagnetic field sensing elements coupled in a differential arrangement inone electronic channel.
 11. The magnetic field sensor of claim 3,wherein the one or more magnetic field sensing elements consist of a onemagnetic field sensing element coupled in an electronic channel.
 12. Amethod of sensing an absolute position of a target object, wherein thetarget object has a first portion having a first quantity of targetfeatures and a second portion having a second quantity of targetfeatures different than the first quantity, wherein the first and secondportions are proximate and mechanically fixed together, wherein thetarget object, including the first and second portions, is capable of amovement, wherein the method comprises: generating a first magneticfield signal responsive to the movement of both the first and secondportions; using the first magnetic field signal to generate a positionvalue indicative of the absolute position; and generating an outputsignal from the magnetic field sensor indicative of the absoluteposition.
 13. The method of claim 12, wherein the absolute position ofthe target object comprises an absolute angle of a rotation of thetarget object.
 14. The method of claim 12, further comprising:generating a maximum peak-to-peak value indicative of a maximumpeak-to-peak value of the first magnetic field signal, wherein the usingthe first magnetic field signal comprises: measuring an amplitude of themagnetic field signal; comparing the amplitude of the magnetic fieldsignal with the maximum peak-to-peak value; and generating an amplitudesignal indicative of the absolute position in accordance with thecomparing
 15. The method of claim 14, wherein the using the firstmagnetic field signal further comprises: decoding the amplitude signalto generate a position signal indicative of the absolute position. 16.The method of claim 14, further comprising: generating a second magneticfield signal responsive to the movement of both the first and secondportions; generating a speed signal indicative of a speed of themovement; and generating a direction signal indicative of a direction ofthe movement.
 17. The method of claim 14, wherein the using the firstmagnetic field signal to generate the position value comprises:identifying an amplitude of the first magnetic field signal; generatingan amplitude value indicate of an amplitude of the first magnetic fieldsignal; relating the amplitude value to the absolute position; andgenerating the position value in accordance with the amplitude value.18. The method of claim 14, wherein the one or more magnetic fieldsensing elements comprises three magnetic field sensing elements coupledin at least one differential arrangement in a respective at least oneelectronic channel.
 19. The method of claim 14, wherein the one or moremagnetic field sensing elements consist of two magnetic field sensingelements coupled in a respective two electronic channels.
 20. The methodof claim 14, wherein the one or more magnetic field sensing elementsconsist of three magnetic field sensing elements coupled in adifferential arrangement in one electronic channel.
 21. The method ofclaim 14, wherein the one or more magnetic field sensing elementsconsist of a one magnetic field sensing element coupled in an electronicchannel.
 22. A magnetic field sensor for sensing an absolute position ofa target object, wherein the target object has a first portion having afirst quantity of target features and a second portion having a secondquantity of target features different than the first quantity, whereinthe first and second portions are proximate and mechanically fixedtogether, wherein the target object, including the first and secondportions, is capable of a movement, wherein the magnetic field sensorcomprises: means for generating a first magnetic field signal responsiveto the movement of both the first and second portions; means for usingthe first magnetic field signal to generate a position value indicativeof the absolute position; and means for generating an output signal fromthe magnetic field sensor indicative of the absolute position.
 23. Themagnetic field sensor of claim 22, wherein the absolute position of thetarget object comprises an absolute angle of a rotation of the targetobject.
 24. The magnetic field sensor of claim 22, further comprising:means for generating a maximum peak-to-peak value indicative of amaximum peak-to-peak value of the first magnetic field signal, whereinthe means for using the first magnetic field signal comprises: means formeasuring an amplitude of the magnetic field signal; means for comparingthe amplitude of the magnetic field signal with the maximum peak-to-peakvalue; and means for generating an amplitude signal indicative of theabsolute position in accordance with the comparing
 25. The magneticfield sensor of claim 24, wherein the means for using the first magneticfield signal further comprises: means for decoding the amplitude signalto generate a position signal indicative of the absolute position. 26.The magnetic field sensor of claim 22, further comprising: means forgenerating a second magnetic field signal responsive to the movement ofboth the first and second portions; means for generating a speed signalindicative of a speed of the movement; and means for generating adirection signal indicative of a direction of the movement.
 27. Themagnetic field sensor of claim 22, wherein the means for using the firstmagnetic field signal to generate the position value comprises: meansfor identifying an amplitude of the first magnetic field signal; meansfor generating an amplitude value indicate of an amplitude of the firstmagnetic field signal; means for relating the amplitude value to theabsolute position; and means for generating the position value inaccordance with the amplitude value.
 28. The magnetic field sensor ofclaim 22, wherein the one or more magnetic field sensing elementscomprises three magnetic field sensing elements coupled in at least onedifferential arrangement in a respective at least one electronicchannel.
 29. The magnetic field sensor of claim 22, wherein the one ormore magnetic field sensing elements consist of two magnetic fieldsensing elements coupled in a respective two electronic channels. 30.The magnetic field sensor of claim 22, wherein the one or more magneticfield sensing elements consist of three magnetic field sensing elementscoupled in a differential arrangement in one electronic channel.
 31. Themagnetic field sensor of claim 22, wherein the one or more magneticfield sensing elements consist of a one magnetic field sensing elementcoupled in an electronic channel.
 32. The magnetic field sensor of claim22, further comprising: means for generating a maximum peak-to-peakvalue indicative of a maximum peak-to-peak value of the first magneticfield signal; and means for generating a gain responsive to the maximumpeak-to-peak value.